The change was most striking among those 17 and younger. There are now more Hispanic children in Arizona than White, non-Hispanic children, suggesting the relative size of the Hispanic population could continue growing.

The hot spots of overall state growth were the West Valley, Phoenix and the far southeast Valley in terms of raw numbers. Political observers have been waiting to see where big gains occurred since the Census Bureau released data in December showing that Arizona, with a 25 percent gain, was the fastest-growing state in the nation after Nevada. The biggest growth spots could play a central role in the creation of a new, ninth congressional seat, to be created before the 2012 elections.

Despite the steep overall gains, there were some disappointments for those who view growth as positive.

Some neighborhoods of the Valley - south Phoenix and the near East Valley - posted small declines, partly a sign of further flight to the suburbs.

Phoenix added more population than any other city in the state, growing by 9.4 percent, to 1.4 million. But that still left it slightly behind Philadelphia, which retained its status as the nation's fifth-largest city.

The state's 10-year growth figures were smaller than gains in the 1990s and fell well short of estimates made in the final years of the past decade. That was especially true in most of the largest cities in Maricopa County.

This will likely make city planners rethink projections on how much federal funding for schools, transportation projects and other needs cities can expect to receive based on population, said Tom Rex, an Arizona State University economist who analyzes census data.

"You're adding that onto the already-dire situation that so many of them are in with the recession-caused reductions in their tax revenues," he said. "This is just one more piece of bad news for many of the communities."

Among other highlights from the census:

- West Valley cities added 300,000 residents, a 69 percent increase since 2000. That doesn't include Phoenix, which is largely in the West Valley but stretches eastward as well. By comparison, the East Valley grew 230,000, or 26 percent. Cities in the northeast Valley grew about 18,000, or 7 percent.

- The city of Maricopa had the fastest-growing rate in the state. Its population exploded from barely 1,000 to 43,000, a more than 4,000 percent jump. Phoenix added nearly 125,000 residents and Gilbert added nearly 99,000.

- Pinal County more than doubled in size, but most counties showed far more modest growth rates. Maricopa County added nearly 745,000 residents, a 24 percent increase, while Pima County grew 16 percent. With 3.8 million residents, Maricopa County is the fourth-largest in the nation.

- The Native American and Alaska Native population climbed 16 percent, to 297,000, but its share of Arizonans fell to 4.6 percent. The number of Native American children 17 and younger also declined.

- Arizona is getting older. In 2000, 26 percent of the state's population was 17 or younger. The 2010 census found that 25 percent of Arizona's population fell in that age group.

Overestimation?

Taken as a whole, the new numbers suggest demographers overestimated the state's growth at the height of the housing boom, in part because of tumult in housing data and lags in recognizing a shift in birth and death patterns, experts say. It's unclear how much the Great Recession and the state's immigration-enforcement policies may have altered the final figures.

"I'm a little disappointed that the Hispanic growth isn't bigger than it is," said William Frey, a demographer at the Brookings Institution in Washington, D.C. "(Still) for the first time, Hispanics have contributed more to the state's growth than Whites. That hadn't happened in the '90s or earlier. That's a significant milestone."

Even as the number of Whites statewide grew 20 percent, in Phoenix they actually declined slightly over the decade. Seventy-three percent of Arizona residents identified themselves as White in 2010, compared with 76 percent in 2000.

The population for Phoenix turned out to be smaller than what the Census Bureau had estimated every year since 2005. The 2009 estimate was nearly 150,000 people higher than what the 2010 tally found.

Based on growth estimated at the end of the past decade, Phoenix actually came in about 10 percent lower than expected. By comparison, other large cities nationally so far have been within about 2 percentage points.

The census count of Arizona's population in 2010 was 4 percentage points below previous census estimates. It was the widest such margin in the country.

Rex said that's largely because of the movements of illegal immigrants and faulty assumptions from the housing boom.

"(Illegal immigrants) come here to work," Rex said. "If they've lost their work, they've lost total motivation to be here.

"That, in conjunction with the (2008) employer-sanctions law, made it harder for them to find another job. It seems quite reasonable to expect that a lot of them up and left the state in pretty good numbers."

Frey suspects the effect of immigration laws may be overstated. It may affect new residents moving in to the state, but such numbers are likely relatively small, he said.

William Schooling, Arizona's demographer for the past two years, said the state's own estimates were skewed by overreliance on misleading housing information, a method he is now changing.

The Census Bureau similarly leans heavily on births and deaths, which are often reported too slowly to reflect the type of sudden shift that apparently happened at the end of the decade, said Schooling, who once headed the bureau's population-estimates division.

"Overall, our growth for the decade is huge, but we know it's a multipart story," Schooling said. "It was huge and then tapered off."

Rex suspects the state population actually shrank on an annual basis for the first time since the 1930s. If so, that would match a pattern in Florida and Nevada, two historically high-growth states where population gains skidded to a halt at the end of the past decade.

Last month, Robert Groves, director of the Census Bureau, could not explain why Arizona proved so challenging, but he promised such surprises would be studied.

The 2010 census confirmed that Arizona remains a bellwether of sorts for national trends, some experts say.

"(Arizona) is a fast-growing state, and it's a place that's at the nexus of the future of America," Frey said.

"You're gaining new immigrants. You're getting people who are starting out their lives and finding it's too expensive to live in California.

"You're still getting retirees, which is going to be a huge group as the Baby Boomers begin to retire. The issues that are going to be on the front burner of a lot of places of the country are going to be first seen in Arizona."